U.S. patent number 6,650,493 [Application Number 09/795,404] was granted by the patent office on 2003-11-18 for pulsed write current adapted for use with a field maintenance current in a data storage device.
This patent grant is currently assigned to Seagate Technology LLC. Invention is credited to Housan Dakroub.
United States Patent |
6,650,493 |
Dakroub |
November 18, 2003 |
Pulsed write current adapted for use with a field maintenance
current in a data storage device
Abstract
An apparatus and method for writing data to a magnetizable
recording medium in the form of spaced-apart magnetic flux
transitions forming magnetization vectors having alternating
magnetic orientations and selected lengths. A write element
adjacent the medium includes a leading edge and a trailing edge
forming a write gap which, when the write element is activated by
an electric current, provides a write field for selectively
magnetizing the magnetizable medium. A write driver circuit is
responsive to a data input stream in providing a write current
activating the write element, the write current comprising a pulse
current in a phased relationship with a continuous current.
Inventors: |
Dakroub; Housan (Oklahoma City,
OK) |
Assignee: |
Seagate Technology LLC (Scotts
Valley, CA)
|
Family
ID: |
22714546 |
Appl.
No.: |
09/795,404 |
Filed: |
February 28, 2001 |
Current U.S.
Class: |
360/46;
G9B/5.033; 360/45; 360/50 |
Current CPC
Class: |
G11B
5/012 (20130101); G11B 5/09 (20130101); G11B
5/02 (20130101); G11B 19/02 (20130101); G11B
2005/001 (20130101) |
Current International
Class: |
G11B
5/09 (20060101); G11B 5/012 (20060101); G11B
005/09 () |
Field of
Search: |
;360/40,44,45,46,48,50,51,68,119,41,31,61 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Hudspeth; David
Assistant Examiner: Figueroa; Natalia
Attorney, Agent or Firm: Cesari; Kirk A.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATION
This application claims priority to U.S. Provisional Application
Ser. No. 60/193,674 filed Mar. 31, 2000.
Claims
What is claimed is:
1. A method for using a data storage device including a write
element responsive to a write current for magnetically recording
data to a magnetizable medium in the device as a sequence of
magnetic flux transitions, the method comprising steps of: (a)
generating a write field with the write element; (b) moving the
magnetizable medium through the write field; and (c) adapting the
write current responsive to a data stream input for activating the
write element to magnetically orient a first area of the medium in
a first direction, the write current comprising a pulse current in
a predetermined phase relationship with a continuous current, and
reversing the write current in response to the data stream input to
magnetically orient a second area of the medium in a second
direction, whereas the reversing of the write current is
implemented such that a steady-state current does not occur during
the reversal of the write current.
2. The method of claim 1 wherein the reversed write current of the
adapting step (c) is applied during a transition window comprising
a time such that a portion of the first area remains within the
write field so that a portion of the first area is magnetically
reoriented by the reversed write current, the remaining portion of
the first area having retained the first magnetization and
traversed beyond the write field comprising a magnetization vector
of a predetermined data bit length.
3. The method of claim 1 wherein the pulse current and the
continuous current are not reversed at the same time.
4. The method of claim 2 wherein a time equal to or less than the
transition window is used to perform one or more circuit switching
processes in order to reverse the write current.
5. The method of claim 2 wherein the pulse current is reversed at a
time when the continuous current, previously reversed, is about
zero.
6. The method of claim 4 wherein the write current can be
discontinuous for a time equal to or less than the transition
window without producing unrecorded gaps in the magnetizable
medium.
7. A data handling device adapted for receiving a data input stream
from a host computer and storing the data, comprising: a rotatable
disc having a magnetizable medium storing the data as several
sequential magnetization vectors in an alternating magnetic
orientation; a write element operably adjacent the disc generating
a write field for selectively magnetizing the magnetizable medium;
a write driver circuit adaptively responsive to the data input
stream and imparting a write current to the write element to
magnetically orient the magnetizable medium in a magnetically
oriented first direction when writing the data input stream to the
disc, the write driver circuit comprising: a first source
responsive to the data input stream for imparting a continuous
current to the write element; a second source responsive to the
data input stream for imparting a pulse current to the write
element; a delay timer phasing the responses of the first and
second sources; the write driver circuit being further configured
to reverse the write current in response to the data input stream
to impart a second area of the magnetizable medium in a
magnetically oriented second direction, the write driver circuit
configured such that a steady-state current does not occur during
the reversal of the write current.
8. The data handling device of claim 7 wherein the delay timer
phases the responses such that the pulse current is reversed at a
time when the continuous current, previously reversed, is about
zero.
9. The data handling device of claim 7 wherein the write driver
utilizes the transition window to electrically switch the circuit
to reverse the write current.
10. The data handling device of claim 7 wherein the continuous
electrical continuity between the pulse current and the write
element permits full rail-to-rail voltage pulses to the write
element.
Description
FIELD OF THE INVENTION
This invention relates generally to the field of magnetic or
magneto-optic data storage devices, and more particularly but not
by way of limitation, to improving data transfer rate performance
by writing data with a magnetic field to a magnetizable medium
using a write driver circuit providing a write current comprising a
field reversing pulse current in phased relationship with a field
maintenance continuous current.
BACKGROUND OF THE INVENTION
Disc drives are used as primary data storage devices in modern
computer systems and networks. A typical disc drive comprises one
or more rigid magnetizable storage discs which are rotated by a
spindle motor at a high speed. An array of read/write heads
transfer data between tracks of the discs and a host computer. The
heads are mounted to an actuator assembly which is positioned so as
to place a particular head adjacent the desired track.
Each of the discs is coated with a magnetizable medium wherein the
data is retained as a series of magnetic domains of selected
orientation. The data are imparted to the data disc by a write
element of the corresponding head. The data thus stored to the disc
are subsequently detected by a read element of the head. Although a
variety of head constructions have been utilized historically,
magneto-resistive (MR) heads are typically used in present
generation disc drives. An MR head writer uses a thin-film
inductive coil arranged about a ferromagnetic core having a write
gap. As write currents are passed through the coil, a magnetic
write field (sometimes referred to as the "write bubble") is
established emanating magnetic flux lines from the core and
fringing across the write gap. The flux lines extend into the
magnetizable medium to establish magnetization vectors in selected
directions, or polarities, along the track on the data disc.
Magnetic flux transitions are established at boundaries between
adjacent magnetization vectors of opposite polarities.
To write a computer file to disc, the disc drive receives the file
from the host computer in the form of input data which are buffered
by an interface circuit. A write channel encodes and serializes the
data to generate a data input stream that can be represented as a
square-wave type signal of various lengths between rising and
falling signal transitions.
A write driver circuit uses the data input stream to generate a
write current which is applied to the write head, creating the
write bubble that writes the encoded data to the magnetizable
medium of the selected disc. The write current both reverses the
polarity of the write bubble, creating the magnetic flux
transitions, and sustains a given polarity between successive
magnetic flux transitions.
Conventional write drivers employ continuous write currents.
Continuous current writing is well suited for the relatively
steady-state conditions between successive magnetic flux
transitions. It is relatively difficult, however, to impart the
magnetic flux transitions with continuous current writing,
particularly at higher data transfer rates. This is due to the
transitory rise/fall characteristics (sometimes referred to as slew
rate) associated with reversing the polarity of a continuous write
current.
Some write drivers employ pulse write currents. Pulse current
writing is well suited for imparting the magnetic flux transitions.
By using the data input stream to trigger a series of very short
duration, discrete pulse currents, flux transitions with a
relatively better edge definition can be created. However,
sustaining the write current with only a pulse write driver between
successive magnetic flux transitions can be problematic, especially
over relatively long bit cell lengths.
There exists a need for improvements in the art to enhance write
driver performance at ever-increasing data transfer rates, so as to
better draw on the benefits of both types of write drivers.
SUMMARY OF INVENTION
The present invention provides an apparatus and an associated
method for improving data transfer rate performance by writing data
with a magnetic field to a magnetizable medium using a write driver
circuit providing a write current comprising a field reversing
pulse current in phased relationship with a field maintenance
continuous current.
In one aspect of the present invention a method is provided for
magnetically recording data to a magnetizable medium as a sequence
of magnetic flux transitions. The method comprises providing a
write element responsive to a current for generating a write field
magnetizing the magnetizable medium. The method further comprises
moving the magnetizable medium relative to the write element. The
method further comprises providing a write current adaptively
responsive to a data stream input for activating the write element
to magnetically orient a first area of the medium in a first
direction, the write current comprising a pulse current in a phased
relationship with a continuous current. The method further
comprises reversing the write current in response to the data
stream input to magnetically orient a second area of the medium in
a second direction.
In reversing the write current, the method applies the reversed
write current generally during a transition window such that a
portion of the first area remains within the write field so that a
portion of the first area is magnetically reoriented by the
reversed write current, the remaining portion of the first area
having retained the first magnetization and traversed beyond the
write field comprising a magnetization vector of a desired data bit
length. More particularly, the maximum time associated with the
transition window disposes the second area contiguous with the
first area with no unrecorded gap therebetween.
In another aspect of the present invention a disc drive storage
device is provided adapted for receiving a data input stream from a
host computer and writing the data to storage. The disc drive
storage device comprises a rotatable disc having a magnetizable
medium storing the data as sequential magnetization vectors in
alternating magnetic orientation. The disc drive storage device
further comprises a write element operably adjacent the disc
generating a write field for selectively magnetizing the
magnetizable medium. The disc drive storage device further
comprises a write driver circuit adaptively responsive to the data
input stream and imparting a write current to the write element to
magnetically orient the magnetizable medium in writing the data
input stream to the disc, the write driver circuit comprising: a
first source responsive to the data input stream for imparting a
continuous current to the write element; a second source responsive
to the data input stream for imparting a pulse current to the write
element; and a delay timer phasing the responses of the first and
second sources.
The disc drive storage device write driver imparts a write current
to magnetically orient a first area of the magnetizable medium in a
first direction, and imparts a reversed write current to
magnetically orient a second area of the magnetizable medium in a
second direction, the reversed write current being imparted during
the transition window.
These and other features and benefits will become apparent upon a
review of the following figures and their accompanying detailed
description.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view of a disc drive constructed in accordance
with a preferred embodiment of the present invention.
FIG. 2 is a diagrammatic representation of a portion of the disc
drive of FIG. 1 showing the manner in which data are written to and
read from the discs of the disc drive of FIG. 1.
FIG. 3 is a diagrammatic representation of the write element shown
in FIG. 2 operably adjacent a portion of the magnetizable medium on
the corresponding disc of the disc drive, showing the write bubble
formed by subjecting the write element to a write current.
FIG. 4 is a graphical representation of the ideal response of an
ideal write driver to the data input stream.
FIG. 5 is a graphical representation of a conventional continuous
current write driver.
FIG. 6 is a graphical representation of a conventional pulse
current write driver.
FIG. 7 is a diagrammatic representation similar to FIG. 3 of the
write element with the write bubble activated at time (t1).
FIG. 8 is a diagrammatic representation of the write element of
FIG. 7 at a subsequent time (t.sub.2) when the write bubble is
momentarily discontinuous.
FIG. 9 is a diagrammatic representation of the write element of
FIG. 8 illustrating the stamp and trim method of pulse writing.
FIG. 10 is a diagrammatic representation of the write element of
FIG. 7 illustrating a case where the write bubble has been
discontinuous such that no subsequent magnetization occurs before
the magnetized medium leaves the write bubble.
FIG. 11 is a diagrammatic representation of the write element of
FIG. 10 at a subsequent time when the write bubble magnetizes the
medium with a gap of unrecorded medium formed between the adjacent
data bits.
FIG. 12 is a graphical representation of the write current produced
by a write driver constructed in accordance with the present
invention, also illustrating the component continuous current and
the pulse current that together form the write current.
FIG. 13 is a schematic representation of a write driver circuit
constructed in accordance with the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to the drawings in general, and more particularly to FIG.
1, shown therein is a plan representation of a disc drive 100
constructed in accordance with the present invention. The disc
drive 100 includes a base deck 102 to which various disc drive
components are mounted, and a cover 104 (partially cut-away) which
together with the base deck 102 and a perimeter gasket 105 form an
enclosure providing a sealed internal environment for the disc
drive 100. Numerous details of construction are not included in the
following description because they are well known to a skilled
artisan and are unnecessary for an understanding of the present
invention.
Mounted to the base deck 102 is a spindle motor 106 to which a
plurality of discs 108 are stacked and secured by a clamp ring 110
for rotation at a high speed in direction 111. Adjacent discs are
typically separated by a disc spacer (not shown). An actuator 112
pivots around a pivot bearing 114 in a plane parallel to the discs
108. The actuator 112 includes an actuator body 115 that is
supported by the pivot bearing 114. The actuator body 115 has
actuator arms 116 (only one shown) that support load arms 118 in
travel across the discs 108 as the actuator arms 116 move within
the spaces between adjacent discs 108. The load arms 118 are flex
members that support data transfer members, such as read/write
heads 120, with each of the read/write heads 120 adjacent a surface
of one of the discs 108 and maintained in a data reading and
writing spatial relationship by a slider (not shown) which operably
supports the read/write head 120 on an air bearing sustained by air
currents generated by the spinning discs 108.
Each of the discs 108 has a data storage region comprising a data
recording surface 122 divided into concentric circular data tracks
(not shown). Each of the read/write heads 120 is positioned
adjacent a respective desired data track to read data from or write
data to the data track. The data recording surface 122 can be
bounded inwardly by a circular landing zone 124 where the
read/write heads 120 can come to rest against the respective discs
108 at times when the discs 108 are not spinning. The data
recording surface 122 can similarly be bounded outwardly by an
overshoot cushion zone 126 beyond the outermost data track.
The actuator body 115 is pivotally positioned by a voice coil motor
(VCM) 128 comprising an electrical coil 130 and a magnetic circuit
source such as a magnet assembly 131. The magnet assembly 131
conventionally comprises one or more magnets supported by magnetic
poles to complete the magnetic circuit. When controlled current is
passed through the actuator coil 130, an electromagnetic field is
set up which interacts with the magnetic circuit of the magnet
assembly 131 to cause the actuator coil 130 to move. As the
actuator coil 130 moves as supported by a yoke 133 portion of the
actuator body 115, the actuator body 115 pivots around the pivot
bearing 114, causing the read/write heads 120 to travel across the
discs 108. A flex assembly facilitates electrical communication
between the actuator assembly 112 and a disc drive printed circuit
board, such as can be mounted to the underside of the base deck 102
(not shown). The flex assembly includes a write driver circuit 134
which electrically interfaces with the heads 120.
FIG. 2 diagrammatically illustrates a portion of the disc drive of
FIG. 1, particularly showing the manner in which data are
transferred between a host computer and the discs 108. A data
communication channel 135 includes a write channel 136 which
encodes and serializes input data forming a data stream that is
input to the write driver 134 of a preamplifier/driver circuit 137.
As discussed below, the write driver circuit 134 applies a write
current to a write element 140 of the selected head 120 to write
the data stream to the respective disc 108. To read previously
stored data, a detection amplifier 141 of the preamp 137 applies a
bias current to an MR read element 142 and transduces the
characteristic magnetization of the disc 108, forming a read back
signal associated with changes in voltage across the read element
142. The detection amplifier 141 conditions the read back signal
that is input to a read channel 144 of the data communication
channel 135.
FIG. 3 provides a diagrammatic representation of the write element
140 of FIG. 2 in conjunction with the respective disc 108. The disc
108 includes a magnetizable medium 148 coating on a substrate 150.
Note that the magnetizable medium 148 is moving in the direction
111 in accordance with the operable disc 108 rotation. The
magnetizable medium 148 magnetically stores the data as a series of
magnetization vectors of a defined bit length, with orientations
generally aligned in directions along the data tracks.
The write element 140 includes a ferromagnetic core 152 about which
a conductor 154 is wound to form a coil 156. When a write current
is passed through the conductor 154, magnetic flux lines are
established in the core 152 that traverse a write gap 158,
generating a write field 160 (or "write bubble" 160) of sufficient
strength to magnetically orient the enveloped portion of the
magnetizable medium 148.
Write currents in a first direction, for example, serve to
magnetically orient the magnetizable medium 148 along the direction
represented by magnetization vector 162. Write currents in an
opposite direction thereby orient the magnetizable medium 148 in
the direction opposite to magnetization vector 162. The core 152
has a leading edge 164 and a trailing edge 166, forming the write
gap 158 therebetween. The write bubble 160 magnetizes medium 148
beyond the gap 158, as indicated by the leading and trailing edges
165, 167, respectively, of the write bubble 160.
Thus, in the most general sense the write driver 134 (FIG. 2) is
responsive to the data input stream in sending a write current to
the write element 140 of the read/write head 120. FIG. 4
illustrates the ideal response, I.sub.IDEAL, of an ideal write
driver. Note that in the ideal case, for each data input stream
cell boundary, such as 168, 170, 172, the write driver responsively
forces an instantaneous current reversal 174, 176, 178. However,
physical constraints of the components from which a write driver
circuit is constructed preclude the possibility of such an ideally
responsive write driver. For example, switches used for reversing
write current direction are typically formed from transistors,
which have inherent structural, or parasitic, capacitances
preventing an instantaneous opening or closing in response to a
control signal. Furthermore, conventional circuit switching
arrangements comprise numerous switches operating cooperatively,
thus compounding the difficulties that prevent attaining the ideal
response.
FIG. 5 illustrates a typical response of a conventional write
driver employing a continuous write current, Ic. In comparison to
the ideal case of FIG. 4, the continuous write current Ic is
relatively slow to respond, as indicated by the characteristic
transitory slew rate determining the current reversals 180, 182,
184 in response to the data cell boundaries 168, 170, 172. Although
relatively easy and inexpensive to construct, the characteristic
slow response limits the use of a continuous current write driver
in high speed and high density data transfers.
FIG. 6 illustrates an alternative approach wherein a write driver
employing a pulse write current, I.sub.p, is used in a "stamp and
trim" method of data writing. Although the pulse write current
I.sub.p offers a fast response and a superior edge form to the
current reversals, where (as in FIG. 6) the bit length is greater
than the pulse width, then the pulse write current I.sub.p is
incapable of sustaining the write bubble 160 between adjacent
magnetic flux transitions corresponding to the data cell boundaries
168,170,172.
Modifications to the continuous current write driver and/or to the
pulse current write driver can improve their suitability for use
individually or in combination in a write driver circuit. Such
modifications, however, entail higher circuit complexity and cost.
The present invention provides a write driver employing a simple
and inexpensive continuous write current circuit in a novel phased
relationship with a simple and inexpensive pulse write current
circuit, providing an effective and efficient dual stage write
driver 134.
One aspect of the present invention lies in the advantageous
solution of a well-known problem associated with the
unpredictability of reversing a continuous current. As noted
before, switches used to reverse the write current have inherent
characteristics preventing ideal opening and closing performance.
Many attempts have been made to adequately sequence and/or
compensate for the simultaneous opening and closing of pairs of
switches such as are used in a common H-bridge arrangement. In such
an arrangement, when one switch opens or closes before the
complementary switch, the write current is momentarily discontinued
due to the open circuit. This condition momentarily deactivates the
write bubble 160.
FIG. 7 is a view similar to FIG. 3, illustrating the medium 148 in
the write bubble 160 being instantaneously magnetized. The trailing
edge of the write bubble 160 at this instantaneous time is denoted
(t.sub.1). If the write bubble 160 is momentarily deactivated at a
time immediately subsequent to time (t.sub.1), the medium 148 will
nevertheless retain its prior magnetization from time (t.sub.1).
FIG. 8 illustrates the read/write head 140 at a subsequent time
(t.sub.2) (former location of the now deactivated write bubble 160
shown as phantom line). The former location of the write bubble
trailing edge 167 is denoted (t.sub.2).
Thus, there is an interval of opportunity after time (t.sub.1)
during which the write current can be noncontinuous and still avoid
unrecorded medium 148. Namely, the write current must be
reactivated before the magnetized medium 148 from (t.sub.1) reaches
the trailing edge of the write bubble 160. For example, FIG. 9
illustrates the write current being reactivated instantaneously at
time (t.sub.2). In this case, the newly magnetized medium overlaps
a portion of the previously magnetized medium 148 at time
(t.sub.1). This is analogous to the "stamp and trim" methodology
generally associated with pulse current writing. It will be noted
that the example of FIG. 9 illustrates a reactivated write current
of opposite polarity, forming a magnetic flux transition at the
boundary. Alternatively, the reactivated write current can be of
the same polarity, for example, to extend the bit length longer
than the write bubble 160.
If, however, as in FIG. 10 at time (t.sub.2) the leading edge of
the magnetized medium 148 from time (t.sub.1) reaches the trailing
edge of the write bubble 160, then subsequent magnetization will
result in unrecorded medium 148 being formed between the first and
second magnetized regions. For example, FIG. 11 illustrates the
write current reactivating the write bubble 160 at time (t.sub.3),
magnetizing a portion of the medium 148 that does not overlap and
is not contiguous with the previously magnetized medium 148 at time
(t.sub.1).
Therefore, the interval of opportunity, (t.sub.d), or "transition
window," is defined as that time that is less than or equal to
(t.sub.2 -t.sub.1). For a given (t.sub.1), (t.sub.2) is defined
exactly as the time it takes the magnetized area from (t.sub.1) to
traverse the write bubble 160. During this transition window
(t.sub.d) the write current can be discontinuous, such as from
circuit switching, and the write driver 134 can effectively
reactivate the write bubble 160 and continue to write data without
producing gaps of unrecorded medium 148 between adjacent data bits.
As discussed previously, using a pulse write current to activate
the write bubble 160 results in the fastest response and best data
bit edge form. But using a continuous write current best sustains
the write bubble 160 polarity between long current reversal times
associated with long bit times. The present invention provides a
write driver 134 making optimal use of both types of write
currents, in a novel phased relationship therebetween.
The present invention thus negates the adverse transitory
characteristics associated with reversing a continuous write
current. These transitory characteristics, such as the slew rate
delays and circuit switching discontinuities, are of no effect
because the magnetizable medium 148 retains the prior magnetization
until such time that the write current imparts the magnetic flux
transition on a desired portion of the previously magnetized medium
148. In fact, the write driver current switching circuits can make
use of any part or all of the transition window, (t.sub.d), to
perform the overall current switching processes. This permits the
use of relatively simpler and less expensive switching circuitry in
the high-speed write driver 134 of the present invention.
FIG. 12 is a graphical representation of the write current I.sub.w
produced by a write driver 134 (FIG. 2) constructed in accordance
with the present invention. The write current I.sub.w is formed
from the combination of a continuous write current I.sub.c with a
pulse write current I.sub.p. The write driver 134 reverses the
continuous write current I.sub.c at the data cell boundary, and
reverses the pulse write current I.sub.p at a selected time,
illustrated by the interval denoted "t" in FIG. 12. Thus, the pulse
current I.sub.p and the continuous current I.sub.c are preferably
not reversed at the same time. More preferably, the pulse current
I.sub.p is reversed when the continuous current, I.sub.c,
previously reversed, is nominally zero or thereafter within the
transition window. In this manner the write current I.sub.w will
reverse faster and with relatively less power dissipation in
reversing from 0 amps to I (+/-) rather than from (+/-) I to (-/+)
I. So long as (t) is within the transition window (t.sub.d), as
defined above, then the medium 148 will be continuously recorded
without gaps between adjacent data bits.
This manner of a phased reversing of the continuous and pulse
currents can be used to optimize the current switching capability
of the write element 140. That is, the write element 140 is
characterized by a current switching capability that is directly
related to the initial state of the continuous current at the time
the pulse current is reversed. Thus, the write element 140
switching capability is optimal at or after the time that the
continuous current I.sub.c, previously reversed, is nominally zero,
and within the transition window. Similarly, this phased reversing
is applicable to the power dissipation of the write driver 134 and
of the write element 140, which is likewise optimal when the pulse
current I.sub.p is reversed at the time or after the time that the
continuous current I.sub.c, previously reversed, is nominally zero,
and within the transition window. Furthermore, this phased
reversing is applicable to the write driver 134 supply current,
which is optimal when the continuous and pulse currents I.sub.c,
I.sub.p are not reversed simultaneously.
FIG. 13 is a schematic illustration of a write driver 134
constructed in accordance with the present invention. A source 224
is connected in parallel with a source 226 to receive the data
input stream. The sources 224, 226 have differential outputs 228,
230 and 232, 234 that are electrically connected to combine
respective output currents of each to produce the write current
I.sub.w.
The source 224 can comprise a conventional continuous write driver
circuit to generate the continuous write current I.sub.c of FIG.
12. Such a slow-switching write driver circuit is relatively
uncomplicated and inexpensive. Advantages of such a write driver
circuit are, for example, that the interconnect transmission lines
can be terminated without loss of headroom, since the peak
reversing current is provided by the pulse current I.sub.p circuit.
Also, as discussed above, relatively low power is consumed by the
reversing of the continuous current I.sub.c slowly.
The current source 226 can similarly comprise a conventional pulse
write driver circuit to generate the pulse write current I.sub.p of
FIG. 12. For example, the current source 226 of FIG. 13 comprises a
pulse generator 246. More generally, the pulse write current
I.sub.p can be generated by a class of circuits that generate
pulses only. Alternatively, pulse generator 246 can comprise a
conventional pulse generator capable of generating a selectively
variable pulse width. Advantages of such circuits are, for example,
the fast response and turn-off times, full rail to rail operation
permitting the use of saturated switches, and lower power
requirements permitting the use of faster transistors. Note also
that termination transistors 235 are necessary only on the
slow-switching source 224, so that the maximum switching voltage is
not limited in the fast-switching source 226.
Finally, a delay timer 248 provides a phased relationship between
the reversing of the continuous write current I.sub.c of the
current source 224 and the triggering of the pulse write current
I.sub.p of the current source 226. So long as the time delay
provided by the delay timer 248 is within the transition window
(t.sub.2 -t.sub.1), as defined above, the pulse current I.sub.p
will magnetize the medium 148 to define the data bit edge before
the previously recorded medium 148 leaves the write bubble 160, so
that no unrecorded gaps are formed between adjacent data bits.
Alternatively, the delay timer 248 can provide a selectively
variable time delay.
Overall, the write driver 134 of the present invention, as
illustrated in FIGS. 12-13, offers enhanced high speed data writing
performance because, in part, current reversals are not dependent
upon the transitory nature of the continuous write current I;
because data bit edges are optimized by the steep transition
characteristics of the pulse current write; and because the
continuous current writer can sustain the write bubble 160 between
magnetic flux transitions.
Because the write driver 134 relies only on the fast pulse I.sub.p
to reactivate the write bubble 160 (in extending the bit or
starting the next bit) it is of no concern what any instantaneous
write current I.sub.w the write driver 134 provides during the
previously recorded transition interval. Therefore, during the
transition window (t.sub.2 -t.sub.1) the write driver 134 can be
optimized on the basis of effectively and efficiently switching
transistors in preparation for the fast pulse I.sub.p. That is, the
present invention permits the use of simple switching arrangements
that were heretofore incapable of writing at high data transfer
rates.
Thus, the write driver 134 of the present invention employs a write
current comprising a field reversing pulse current in a phased
relationship with a field sustaining continuous current. It will be
noted that the write current I.sub.w can be discontinuous without
producing unrecorded gaps in the magnetizable medium 148.
Particularly, the write current I.sub.w can be discontinuous for a
time equal to or less than the transition window without producing
unrecorded gaps in the magnetizable medium. This permits the use of
the transition window to advantageously design novel fast-acting
write driver circuits form conventional, relatively inexpensive and
uncomplicated sources.
Alternatively characterized, a first embodiment of the present
invention is a method for using a write element responsive to a
write current for magnetically recording data to a magnetizable
medium 148 as a sequence of magnetic flux transitions. The method
includes generating a write field with the write element while
moving the magnetizable medium 148 through the write field. The
write current is adapted responsive to a data stream input for
activating the write element to magnetically orient a first area of
the medium 148 in a first direction, the write current comprising a
pulse current in a predetermined phase relationship with a
continuous current, and reversing the write current in response to
the data stream input to magnetically orient a second area of the
medium 148 in a second direction opposed to the first direction.
Preferably, the reversals 174,180 of the pulse current and of the
continuous current have a non-zero phase offset.
In a second embodiment, the foregoing method is modified so that
the reversed write current is applied during a transition window
comprising a time such that a portion of the first area remains
within the write field so that a portion of the first area is
magnetically reoriented by the reversed write current, the
remaining portion of the first area having retained the first
magnetization and traversed beyond the write field comprising a
magnetization vector 162 of a desired data bit length.
In a third embodiment, the foregoing method is modified so that a
time equal to or less than the transition window is used to perform
one or more circuit switching processes in order to reverse the
write current. Preferably, the pulse current is reversed at a time
when the continuous current, previously reversed, is about zero
(i.e. has a negligible magnitude). Optionally, the write element is
characterized by a current switching capability directly
proportional to the initial state of the continuous current at the
time the pulse current is reversed and such that the write element
switching capability is optimal after the continuous current is
nominally zero.
In a fourth embodiment, the foregoing method is performed so that
almost no unrecorded gaps are formed in the magnetizable medium 148
despite substantial discontinuities in the write current (i.e. up
to about the duration of the transition window).
In a fifth embodiment, the present invention is a data storage
device (e.g. a magnetic tape drive or magneto-optic disc drive 100)
adapted for receiving a data input stream from a host computer and
storing the data. The device includes a magnetizable medium 148
storing the data as sequential magnetization vectors 162 in
alternating magnetic orientation and a write element operably
adjacent the medium 148 generating a write field for selectively
magnetizing the it. The device also includes a write driver circuit
134 adaptively responsive to the data input stream and imparting a
write current to the write element to magnetically orient the
medium 148. The circuit includes a first source 224 responsive to
the data input stream for imparting a continuous current to the
write element, a second source 226 responsive to the data input
stream for imparting a pulse current to the write element, and a
delay timer 248 establishing a predetermined phase relationship in
the responses of the first and second sources 224,226.
In a sixth embodiment, the foregoing device is modified so that the
write driver 134 imparts a write current to magnetically orient a
first area of the magnetizable medium 148 in a first direction, and
wherein the write driver 134 imparts a reversed write current to
magnetically orient a second area of the magnetizable medium 148 in
a second direction. The reversed write current is imparted during a
transition window comprising a time such that a portion of the
first area remains within the write field so that a portion of the
first area is magnetically reoriented by the reversed write
current, the remaining portion of the first area having retained
the first magnetization and traversed beyond the write field
comprising a magnetization vector 162 of a desired length. The
delay timer 248 provides a phased response time that is less than
or equal to the transition window. The delay timer 248 can
optionally be selectively variable and/or can phase the responses
such that the pulse current is reversed at a time when the
continuous current, previously reversed, has a negligible
magnitude.
In a seventh embodiment, the foregoing device is modified so that
the write driver 134 utilizes the transition window to electrically
switch the circuit to reverse the write current. The write driver
134 is optionally characterized by a power dissipation that is
directly related to the initial state of the continuous current
such that the write driver 134 power dissipation is optimal when
the pulse current is reversed at the time or after the time that
the continuous current, previously reversed, is about zero.
In an eighth embodiment, the foregoing fifth embodiment is instead
modified so that the continuous electrical continuity between the
pulse current and the write element permits full rail-to-rail
voltage pulses to the write element. Most preferably, the pulse
width of the pulse current and the magnitudes of the continuous and
pulse currents are all independently selectively variable. Also,
the write driver 134 supply current is directly related to the
phased reversing of the continuous and pulse currents, such that
the write driver 134 supply current is optimal when the continuous
and pulse currents are not reversed simultaneously.
It will be clear that the present invention is well adapted to
attain the ends and advantages mentioned as well as those inherent
therein. While presently preferred embodiments have been described
for purposes of this disclosure, numerous changes may be made which
will readily suggest themselves to those skilled in the art and
which are encompassed in the spirit of the invention disclosed and
as defined in the appended claims.
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